Electronic bass instrument tube preamplifier

ABSTRACT

Electronic bass register musical instrument tube preamplifier. An in line signal preamplification device which richens the tone of electronically amplified bass register musical instruments. The unit is connected in the signal path between the instrument and the amplifier by the use of a standard ¼″ input jack and a ¼″ output jack. Other effects processors may be placed either before or after the preamplification device. There is one volume control and one overdrive switch, which utilizes a variable current source driving section to further reduce distortion and richen the bass register tone. The variable current drives the plates of ½ of the 12AX7 tube with a 48 VDC plate voltage plate voltage in the overdrive position and a 40 VDC plate voltage in the normal position. Use of the overdrive position causes a premature failure of the 12AX7 tube, so it should be used sparingly. The EBIP is useful for both solid state and tube amplifier applications. It is particularly effective for the electric bass guitar with certain brands of strings. Passive pick-ups are better, and other effects, such as fuzz tone, wah wah pedals, etc have an improved musical tone. Definitions: Paper in oil capacitor: The paper in oil capacitors referred to herein are of the variety produced by high end electronics firms such as Audionote UK.

The Electronic Bass Instrument Preamplifier (hereinafter referred to as EBIP) is an audio preamplifier section for electric bass guitar and other amplified bass register musical instruments. The basis for the EBIP invention is not in the circuit schematic that it uses, but in its use of paper in oil capacitors and in the use of these capacitors combined with a modern thin film capacitor in the circuit. It uses one half of a 12AX7 tube, and there is a switch which allows the tube to be overdriven for a more enhanced effect. The input socket must be isolated from the ground for RFI (radio frequency interference) reasons.

Paper in oil capacitors have not been manufactured for use by the general public since the 1950's, but today there has been a resurgence of their use in high end audio equipment. In the following schematic C1 is a Mylar paper in oil capacitor. C2-C3 consists of two 0.47 uf paper in oil copper foil capacitors in series. C4 is a modern “orange drop” capacitor, and C5 is a ceramic disc capacitor. All resistors are of the ½ watt value. The B+ voltage of 153 VDC is only a typical voltage, and other voltages would work equally as well with some adjustments to the values of R1, R2, and R4. A grounded metal box contains the electronic components of the EBIP.

The circuit contains one volume control in its last stage, and EBIP is designed to be placed in the signal circuit between the instrument and the amplifier.

The heater for the tube needs 6.3 VDC or 12.6 VDC. The heater circuit is not shown in the schematic, but is incorporated herein as is typical in such tube circuits.

BACKGROUND OF THE INVENTION

In or around 1960 a change in the tone of audio amplifiers was apparent. The first transistor radios were being mass produced during this period, and a new process for manufacturing signal capacitors was developed and used. The new capacitors were smaller and easier to mass produce.

Most musical instrument amplifiers were still tube amplifiers at this time, but they began to utilize the modern signal capacitors. This did not affect the tone of musical instruments in the treble register as much as it did musical instruments in the bass register (eg. Tone controls on electric bass guitars no longer changed the tone very noticeably, compared to what they would do when playing through an amplifier made before the advent of the new process signal capacitors.)

In the late 1960's through the 1980's most musical instrument amplifiers began to be produced as solid state amplifiers. These amplifiers were not an improvement of tone, but an improvement in manufacturing process. By the 1980's certain amplifier and effects manufacturers began to introduce 12AX7 tube preamplifier circuits that were fairly effective in making the tone of treble register instruments richer and less distorted. Bass register instruments were not affected to the same extent, and new ways of playing the electric bass (e.g. slap picking, etc.) were developed. Further development of digital effects processors has to some extent improved the tone of bass register instruments, and the preamplifier circuits utilized in Kennedy (U.S. Pat. No. 4,672,671) and Kennedy et al. (U.S. Pat. No. 4,644,289), which makes use of two sides of a 12AX7 tube, creates a richer and less distorted tone, much in the same way as the EBIP invention.

The present invention has been described according to a preferred embodiment thereof. It is understood that modifications can be applied to the form, disposition, and values thereof without exceeding the scope of the EBIP invention.

This is a very unique device in that it can richen the tone of the electric bass guitar, especially in the lower octave and a half on the instrument. It is also very effective for creating a richer tone for other bass register musical instruments. The use of a combination of paper in oil condensers, as described above, with a modern, mass produced thin film one is particularly unique.

With S1 in the overdrive position the tone of an electric bass guitar can become much less distorted at louder volumes. 

1. An electronic bass register musical instrument tube preamplifier. An in line signal preamplification device with a ¼″ input connection and a ¼″ output connection, one volume control, and one tube overdrive switch.
 2. An electronic bass register musical instrument tube preamplifier, as claimed in claim 1, and further including the use of paper in oil signal capacitors in combination with a modern polyester film “orange drop” style capacitor in a 12AX7 preamplifier circuit, as described herein, which richens the tone of bass register musical instrument electronic signals.
 3. An electronic bass register musical instrument tube preamplifier, as claimed in claim 1, and further including the use of a tube overdrive switch, which drives the plates at either 40 VDC or 48 VDC, to further reduce distortion and richen tone.
 4. An electronic bass register musical instrument tube preamplifier, as claimed in claim 1, and further including a source of DC voltage for driving the plates of a 12AX7 tube. (153 VDC typically)
 5. An electronic bass register musical instrument tube preamplifier, as claimed in claim 1, and further including a source of DC voltage for driving the heater in ½ of a 12AX7 tube. (6.3 VDC or 12.6 VDC)
 6. An electronic bass register musical instrument tube preamplifier, as claimed in claim 1, and further including a grounded metal box containing the components contained in the schematic diagram herein to eliminate RFI. 